Pipeling style SDI(FI) pollution index apparatus QZDY-SDI47 analyzer system includes a pressure reducing valve, 47mm membrane filter, diaphragm and some necessary valves, connecting pipes and connecting pieces. The system contains a box of mixed cellulose filter membranes, fully compliant with ASTM methods. Using this device, you only need to prepare a graduated cylinder and stopwatch to measure the SDI value online.

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Description : 

Pollution Index (SDI) value, also known as FI (Fouling Index) value, is one of the important parameters of water quality indicators. It characterizes the content of particles, colloids and other objects in water that can clog various water purification equipment. By measuring the SDI value, the corresponding water purification technology or equipment can be selected. This method is accepted in the industry according to ASTM method 4189-95.

In the process of reverse osmosis water treatment, the SDI value is one of the important indicators to determine the influent water of the reverse osmosis system; it is the main means to check whether the effluent of the pretreatment system meets the requirements of reverse osmosis influent water. Its size is critical to the operational life of the reverse osmosis system.

The SDI value is the attenuation of the flow rate measured through a 47 mm diameter, 0.45 μm pore size microporous membrane. The 0.45 μm pore size membrane was chosen because at this pore size, hard particles of colloidal substances (such as sand, scale, etc.) are more likely to block the membrane. The decay of the flow rate is converted into a number between 1 and 100, this is the SDI value. The lower the SDI value, the less tendency for water to foul the membrane. Considering both economy and efficiency, most reverse osmosis manufacturers recommend that the SDI value of reverse osmosis influent should not be higher than 5.


1)Preferred fittings of reverse osmosis system

2)Designed according to ASTM D4189-95 criterion

3)SDI (FI) value is accurate, timely and online monitoring

4)Detachable quick-release design for quick and convenient membrane replacement

5)Pipeline design for easy online installation

Instruction for use

  • Close water polo valve (2), prevent the water entering the measure apparatus.
  • Install the analyzer’s connected screw (1)at the location to be measured.
  • Open the water inlet ball valve (2) and adjust the pressure to 207KPa.
  • Close the water polo valve (2 )
  • Remove the membrane cartridge. (How to take the membrane filter box: push the outer ring of the quick-connect valve (4) upwards, and the membrane filter box will fall off automatically. Note: When disassembling, the membrane filter box must be held well to prevent the box from falling off and damaging the membrane filter.)
  • After removing, open the membrane box, take out the “O” ring , put the 0.45μm filter membrane on the support plate in the membrane box with tweezers, put the “O” ring in the original position, and cover the membrane box Put the upper cover (6), and tighten the compression screw (5) to an appropriate degree.
  • Insert the membrane filter box into the quick connect valve (4)
  • Open the water inlet ball valve (2) to drive out the air bubbles entrained on the membrane box, close the water inlet ball valve (2), and tighten the compression screw (5).
  • Open the water inlet ball valve (2), and at the same time measure the time t1 required to filter the 500ml water sample at the beginning, and let it continue to filter.
  • Measure the time t2 to filter a 500ml water sample at 5, 10 and 15 minutes (Note: the pressure must be maintained at 207±7KPa during the entire test).
  • Measure the water temperature (Note: The water temperature must remain within ±1°C throughout the measurement period).
  • Calculation of SDI

P30: Blockage index at 207KPa inlet water pressure

Tt: The total measurement time (minutes), usually T15, at this time P30 < 75%, otherwise test T10 or T5, makes P30 < 75%

t1: Time (seconds) required to collect a 500ml water sample initially

t2 : Time (seconds) to collect 500ml water sample after Tt (usually T15)

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